Add flour, sugar, and salt to a mixing bowl. Add cold butter and rub it gently into the flour. Mix in the egg yolk and cold water until soft dough forms.

Shape the dough into a flat disc. Wrap it well and refrigerate for about 20 minutes. Chilling helps the butter stay firm and makes the crust easier to roll.

Lightly flour your work surface. Roll the chilled dough into a circle slightly larger than your tart pan. Work gently and avoid adding too much flour during rolling.

Place the dough inside the tart pan. Press it gently into the bottom and sides. Trim the extra dough around the edges. Prick the bottom several times with a fork.

Preheat your oven to 375°F. Line the crust with parchment paper and add pie weights or dry beans. Bake for about 15 minutes. Remove the weights and bake another 8 minutes.

Warm the milk in a saucepan over medium heat. Whisk egg yolks, sugar, and cornstarch in another bowl. Slowly add warm milk while whisking constantly to prevent lumps.

Return the mixture to the saucepan. Cook over medium heat while whisking constantly. The mixture will become thick and creamy. Remove from heat and stir in vanilla and butter.

Transfer the cream filling to a clean bowl. Cover the surface with plastic wrap to prevent a skin from forming. Let the filling cool until it becomes comfortable to spread.

Spread the cooled cream evenly inside the completely cooled tart crust. Use the back of a spoon to create a smooth surface. Keep the filling level for a neat finish.

Arrange strawberries, blueberries, kiwi, raspberries, and mango over the cream. Start around the outside and work toward the center. Create a simple pattern for a beautiful presentation.

Refrigerate the finished tart for at least 30 minutes. Chilling helps the filling set properly. Slice the tart with a sharp knife and serve it cold or slightly chilled.